Mice are the first step in trying out new drugs that may one day help humans. The problem is that these rodents metabolize drugs in often a very different way than we do, meaning that much of the research in mice can't be applied to humans. Researchers from Stanford University may have found a way around this by creating mice with human livers.

No, they're not attaching comically large organs to tiny rodents, but rather engineering special tiny hybrid livers that they're implanting in "humanized" mice. The scientists grew human liver cells and mouse skin cells together, then coated them in protective peptide. The hybrid livers were then implanted in the mice — leading to the critters having human liver functions, including synthesizing human proteins and metabolizing drugs the way we do — toxic interactions and all.

If this model is successful, the process of designing drugs would be dramatically streamlined.